Radar systems are well known for an ability to detect and track stationary and moving targets, and have achieved wide-spread use in navigation systems for vehicles such as aircraft and shipping. The size, complexity and expense of such systems, however, precludes their use in certain applications, particularly those in which the radar system must be small and light. Such systems are required for example in vehicle collision avoidance, cruise control and air bag deployment systems, collision avoidance and altimeter systems for aircraft and guided missiles, security systems such as intruder alarms and robotic control and guidance systems, for example for use in robotic vacuum cleaners and lawn mowers, in unmanned planetary exploration vehicles and in toys.
Various vehicle collision avoidance systems are described, for example, in more detail in British patent applications Nos: GB 2262829A and GB 2266803A, European patent application No. EP 0605104 A1, and U.S. Pat. No. 5,289,182.
Although radar systems of a relatively small size have been developed for use as speed detectors in motor vehicle traffic control and as proximity detectors in motor vehicles, these systems have generally lacked the performance characteristics necessary for widespread usage in many potential applications, particularly those in which it is necessary to detect and track accurately both stationary and moving objects within the immediate vicinity. Another problem with many known systems is that they require bulky wave guides, which cannot easily be accommodated within, for example, the body of an automobile without adversely affecting the appearance of the vehicle.
Other problems with the radar systems used in known vehicle collision avoidance systems include that the beam width is too large, for example more than 10.degree. at mm wavelengths, so that the radar is unable to distinguish objects less than 17 m apart at a range of 100 m; that the detector and the receiver are sensitive to changes in the ambient temperature; and that they are unable to detect both stationary objects and the velocity of moving objects.
It is an object of the present invention to provide a FMCW (frequency modulated continuous wave) radar system that mitigates at least some of the aforesaid problems.